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In this paper, resolution limits of laser spectroscopy absorption measurements with hollow capillary fibers are investigated. Furthermore, a concept of sensitive near-infrared sensing utilizing hollow fiber directly coupled with vertical-cavity surface-emitting lasers is developed. By performing wavelength modulation spectroscopy, the smallest absorbance that can be detected by the fiber sensor was determined to be [10.sup.-4], limited by a random modulation of the fiber transmission function (modal noise). By mechanically vibrating the fiber, a sensor resolution of [10.sup.-5] in absorbance is achieved. Because the random modulation on the fiber transmission function limits the detection sensitivity, its physical reasons are analyzed. One contribution is found to be the partial integration of the far field, and the amplitude of the spectral features is inversely proportional to the square root of the integrated speckle points number. Therefore, careful design of the fiber-detector outcoupling is necessary. It turned out that incoupling alignment is not of much influence with respect to the spectral background. The residual spectral background is caused by mode-dependent effects and can be lowered by vibrating the fiber mechanically. OCIS codes: 300.6360, 060.2370.

A compact Si-nanowire-based reflective arrayed-waveguide grating (AWG) for dense wavelength-division multiplexing is proposed. At the end of each waveguide in the array, there is an individual photonic crystal (PhC) reflector, which makes the AWG layout design very flexible. All the PhC reflectors are with the same design. With such a design, the total size of the AWG (de)multiplexer is reduced by more than a half. The reflection efficiency of the used PhC reflectors is enhanced by optimizing the taper between the arrayed waveguides and the PhC reflector. A 200 GHz AWG (de)multiplexer is designed and fabricated as an example. The total size is only about 193 [micro]m x 168 [micro]m. OCIS codes: 230.7408, 230.5298.

A cross-slot waveguide geometry provides high confinement of the mode field of both fundamental quasi-TE and quasi-TM modes in geometrically perpendicular slots. A unique possibility to tailor optical mode characteristics such as effective index and confinement factor quite independently for the two polarizations with geometric and material parameters is shown. Nonbirefringent cross-slot geometries are presented. Fabrication related tolerances of the cross-slot geometry for low birefringence operation are studied. Means to externally tune the birefringence by a thermo-optic effect is also analyzed. Fabrication of a cross-slot waveguide test structure is demonstrated. [c] 2009 Optical Society of America OCIS codes: 030.4070, 080.2208, 130.2790, 130.3120, 230.7390, 260.1440.

A periodically poled LiNb[O.sub.3] (PPLN) crystal waveguide has been used to produce up to 200[micro]W of mid-infrared light around 3081 [cm.sup.-1] with a wide tunability range of ~35 [cm.sup.-1]. Two commercial near-infrared diode lasers at 1.064[micro]m (pump) and 1.583 [micro]m (signal) are mixed in a nonlinear optical crystal to achieve difference frequency generation. The 48 mm long directly-bonded quasi-phase-matched (QPM) PPLN waveguide shows a conversion efficiency of 12.3% [W.sup.-1]. Applications in trace gas detection have been demonstrated for ethene, using multipass absorption coupled with wavelength modulation spectroscopy, and cavity enhanced absorption spectroscopy with a lock-in detection scheme: bandwidth reduced sensitivities Of [[alpha].sub.min] = 8 X [10.sup.-9] and 1.6 x [10.sup.-8] [cm.sup.-1] [Hz.sup.-1/2](2[sigma]), respectively, have been achieved. OCIS codes: 140.2020, 190.4223, 190.4360, 280.1120, 300.1030, 300.6340.

We propose a novel scheme for ultrabroadband midinfrared (mid-IR) generation using quasi-phase-matched difference-frequency generation (DFG) in a GaN/[Al.sub.x][Ga.sub.l-x]N based Bragg reflection waveguide (BRW). By optimally tailoring the phase-and group-velocity dispersion properties of symmetric BRWs, we show that the phase-matching condition for a DFG process could be maintained over a broad range of signal wavelengths. This could lead to generation of an ~700 nm broad idler close to 3.26 [micro]m wavelength. Since the idea is based on dispersion compensation using photonic bandgap geometry, we can shift the broadband features to any desired spectral region and for any material system within the constraints imposed by the transparency of nonlinear materials. We also investigate the possibility of broadband mid-IR generation using pump sources with broad spectral width. OCIS codes: 230.7390, 230.1480, 230.7405, 190.4975.

We investigate photonic crystal waveguides that are formed by holes of reduced diameter within a hexagonal lattice of cylindrical airholes in thin freestanding silicon slabs. The waveguides operate in both an even-symmetry bandgap and a partial gap of odd-symmetry modes that form a complete two-dimensional bandgap under the light line. The operating frequency is tuned by the small-hole diameter to fit within the range of both bandgaps and to match a free-space wavelength of 1550 nm. Their narrow bandwidth and low group velocity of light propagation renders the waveguides useful as filters or sensing elements. Because of the strong dependence of the waveguide mode characteristics on structural changes, the highest-precision lithographic fabrication techniques must be applied. OCIS codes: 230.5298, 230.7400, 160.5293.

We investigate the properties of ring resonators that are supported by a two-dimensional photonic crystal waveguide. The proposed structure composed of a photonic crystal ring resonator (PCRR) with four scatters can really function as a wavelength division multiplexer. The significance of the design is that the output waveguide is perpendicular to the ring resonator. We numerically demonstrate that the proposed four-channel PCRR device with 3 x 3 inner dielectric rods can provide a transmission efficiency larger than 92%, a quality factor higher than 3800, and crosstalk of less than -32 dB. of America OCIS codes: 230.5750, 230.7408, 250.5300, 350.4238.

A novel biochemical sensor based on a submicrometer size, high core--cladding index difference, silica core Si--Si[O.sub.2] waveguide with a Bragg grating written in its cladding region is proposed and analyzed. Waveguide parameters are optimized to obtain maximum sensitivity, and for lower refractive index samples, an optimum core width is found to exist for both the TE and the TM mode configurations. Owing to the high index contrast at the Si--Si[O.sub.2] interface, the structure is much more sensitive while operating in the TM mode configuration, showing extremely high sensitivity [200-740 nm refractive index units (RIU)] for the ambient refractive indices between 1.33 and 1.63, which is of the order of most surface plasmon polariton (SPP) based biosensors. Further, unlike SPP based sensors, the proposed structure is free from any metallic layer or bulky prism and hence easy to realize. Owing to its simple structure and small dimensions, the proposed device could be easily integrated with planar lightwave circuits and could be used for lab-on-a-chip applications. OCIS codes: 050.2770, 060.2340, 130.0130, 130.3120, 130.6010.

We propose a new numerical model to analyze heat induced by two-photon absorption and free-carrier absorption, while high intensity optical pulses propagate along silicon-on-insulator (SOI) nanowave-guides (NWGs). Using this model, we demonstrate that such induced heat causes a shift in the amount of wavelength conversion and hence deteriorates the converter output characteristics for pulses in the picosecond regime. The wavelength shift induced by a pulse with maximum input intensity and full width at half-maximum of [I.sub.max] = 1.5 X [10.sup.10] W.[cm.sup.-2] and [T.sub.FWHM] = 30 ps, propagating along a SOI NWG with an effective cross-sectional area of [a.sub.eff] = 0.15 [micro][m.sup.2], is shown to be [DELTA][[lambda].sub.s] = 8 pm. We also demonstrate that such a shift can be compensated by tuning the pump intensity down by approximately 6.33%. OCIS codes: 130.4705, 190.3270, 190.4360, 230.7370, 230.7405.

We present in-depth discussion of the design and optimization of a nanomechanical sensor using a silicon cantilever comprising a two-dimensional photonic crystal (PC) nanocavity resonator arranged in a U-shaped silicon PC waveguide. For example, the minimum detectable strain, vertical deflection at the cantilever end, and force load are observed as 0.0133%, 0.37 [micro]m, and 0.0625 [micro]N, respectively, for a 30 [micro]m long and 15 [micro]m wide cantilever. In the graph of strain versus resonant wavelength shift, a rather linear relationship is observed for various data derived from different cantilevers. Both the resonant wavelength and the resonant wavelength shift of cantilevers under deformation or force loads are mainly a function of defect length change. Results point out that all these mechanical parameters are mainly dependent on the defect length of the PC nanocavity resonator. This new PC cantilever sensor shows promising linear characteristics as an optical nanomechanical sensor. OCIS codes: 230.4685, 350.4238, 280.4788, 140.3945, 230.3990, 130.5296.

There are three recognized low-loss configurations for waveguide laser resonators in which the waveguide is either closed at each end by a plane mirror (dual case I design) or one of the plane mirrors is replaced by a curved mirror at some distance from the guide exit. Some time ago, a variant of the latter design was proposed by exploiting the self-imaging properties of multimode waveguides. The resonator was predicted to produce a [TEM.sub.00]-like output with very low round-trip loss and excellent mode discrimination even though the curved mirror was placed much nearer to the guide exit (making the resonator more compact) than was conventional for achieving those results. In the present work, we show that the desirable features of the above design can be achieved even in a dual case I configuration by using end mirrors with suitable reflectivity profiles. Since there is no free space region between the waveguide and the mirrors, the resonator will have the additional advantages of being compact and portable. Furthermore, the absence of curved mirrors will also facilitate its realization in semiconductor integrated optics technology. OCIS codes: 140.3410, 230.5750, 230.7390, 130.0130.

The design and properties of an evanescent coupling method developed by using a semiconductor antiresonant reflecting optical waveguide and a side-polished fiber is discussed. The newly developed side-coupled fiber semiconductor laser could be applied to design and fabricate hybrid fiber-semiconductor devices.

A standard ion-exchange technique was used for the fabrication of channel optical waveguides in novel Er-doped and Er-Yb co-doped ZnO-containing silicate glasses. Findings reveal the simulation of very large net optical gain for an ideal overlap of the pump and signal optical field in a glass containing at 3% of Er and no Yb.

Dispersion of ground-penetrating radar (GPR) waves can occur when they are trapped in a layer. In this paper, we analyze the modal propagation of GPR pulses through a layer of ice that is overlying water. Dispersed transverse electric (TE) waves that are trapped in the waveguide have larger amplitudes than the critically refracted waves that travel through air, whereas the transverse magnetic (TM) critically refracted waves traveling through air are more dominant than the trapped dispersed TM waves. This can be explained by the leaky waveguide behavior of the ice layer. The reflection coefficients for the waves incident on the ice-water interface show that the TM modes are more leaky than the TE modes. Still, clear dispersion is observed in both cases, which depends on the permittivity and thickness of the ice. Similar to inversion of dispersed Rayleigh waves, these parameters can be estimated by calculating phase-velocity spectra, picking dispersion curves, and inverting the dispersion curves using a combined local and global minimization procedure. Synthetic data show several higher order modes of which separate and combined inversions return the input modeling parameters accurately. Experimental data acquired on a frozen lake show strong dispersion for the TE and TM modes. The phase-velocity spectra of the field data show three TE and four TM modes of which separate and combined inversion of different modes return similar values for the ice thickness and known permittivity of ice. Due to the more leaky behavior of the TM modes, the TE inversion is better constrained and more suitable for inversion. Index Terms--Dispersion, ground-penetrating radar (GPR), ice, inversion, leaky waveguide, transverse electric (TE), transverse magnetic (TM).

Interactions between charged macromolecules (e.g., proteins, nucleic acids, polyelectrolytes) and charged surfaces govern many natural and industrial processes. We investigate here the influence of an applied electric potential on the adsorption of charged polymers, and report the following significant result: the adsorption of certain amine side chain-containing polycations may become continuous, i.e., asymptotically linear (or nearly linear) in time over hours, upon the application of a modest anodic potential. Employing optical waveguide lightmode spectroscopy (OWLS) and an indium tin oxide (ITO) substrate, we show that asymptotic kinetics, and the adsorbed mass at the onset of the asymptotic regime, depend sensitively on polymer chemistry (in particular, side chain volume and charge location), increase with applied potential and ionic strength (conditions favoring a thicker initial layer), and are independent of bulk polymer concentration (suggesting postadsorption events to be rate limiting). X-ray photoelectron spectra reveal a suppressed polymer charge within layers formed via continuous adsorption, but no evidence of electrochemical reactions. We propose a mechanism based on polymer-polymer binding within the adsorbed layer, enabled by suppressed electrostatic repulsion and/or enhanced ionic correlations near the conducting surface, and stabilized by short-range attractive interactions. Continuous adsorption under an applied electric potential offers the possibility of nanoscale films of tailored polymer content realized in a single step. optical waveguide lightmode spectroscopy | poly(L-lysine) | protein adsorption | indium tin oxide

The experimental and theoretical aspects of the interaction of gold nanoshells on a waveguiding structure are studied. The result reveals that the light scattering spectrum of the nanoshells is modified because of the presence of an underlying waveguiding structure.

An integrated optical waveguide refractometer, believed to be novel, is presented. The sensor is based on an antiresonant reflecting optical waveguide and uses the strong attenuation dependence on the refractive index of antiresonant cladding layers as the sensing principle. The theory and the operation of the sensor are discussed in terms of one- and two-dimensional geometry. The theoretical predictions and numerical analysis show that a versatile sensor can be realized. The design trade-offs are discussed, and the sensitivity and measurement range are presented. OCIS codes: 130.3120, 130.6010, 230.7390, 230.0250.

A geometrical modulation-based interferometry (GMI) for a displacement sensor is presented. The implementation of the GMI is based on the suspended optical waveguide displacement sensors (SOWDS's) technology. The interferometry effect of the GMI results from light propagating in geometrically modulated and mutually coupled suspended waveguides with an in-plane degree of freedom. The building block of the suspended waveguides is a single-crystal silicon (SCS) beam with superficial layers comprising a 0.6-[[micro]meter]-thick Si[O.sub.2], 0.4-[[micro]meter]-thick [Si.sub.3][N.sub.4], and 0.6-[[micro]meter]-thick Si[O.sub.2]. The SCS beam is fabricated with a cross section of 1.6 [[micro]meter] x 10 [[micro]meter] and may guide light with wavelength in the 1.3-1.5-[[micro]meter] range. The first Si[O.sub.2] layer serves as a buffer layer that allows light with wavelength in the 0.6-0.9-[[micro]meter] range to be guided in the [Si.sub.3][N.sub.4] layer. This paper discusses the theoretical consideration and the characterizations of a GMI displacement sensor. Index Terms - Integrated optics, integrated opto-MEMS, interferometry displacement sensors, optical displacement sensing, suspended optical waveguides.

A novel compact multichannel integrated optical sensor module is described. Its performance is demonstrated by measurement of the mass adsorption of an analyte molecule to the transducer surface by refractometry in an immunosensor experiment. The signal transduction is achieved by means of chirped grating couplers, which allow simple yet highly functional sensor modules to be built. The experiments were performed with high-sensitivity replicated polycarbonate Ti[O.sub.2] waveguide sensor chips for detecting the binding of rabbit immunoglobulin to immobilized protein A. A resolution of [+ or -]3 pg/[mm.sup.2] surface mass coverage was obtained in a dual-channel module with size 10 cm x 10 cm x 10 cm.

An imaging scheme through scattering media in which parametric image amplification is used is presented. An image of a resolution chart through a solution of latex microspheres with an attenuation of 22 mean free paths is obtained with a resolution of 20 [[micro]meter]. The evolution of the signal-to-noise ratio with respect to the medium attenuation is studied and compared with a rough modeling of the imaging process. Key words: Diffusing medium, parametric amplification, imaging system.

An integrated optic sensor head was proposed for sensing a two-dimensional displacement of a scale consisting of crossed gratings. Two interferometers, crossing each other, are constructed by the integration of two pairs of linearly focusing grating couplers (LFGC's) and two pairs of photodiodes (PD's) on a Si substrate. Four beams radiated by the LFGC's from the sensor head overlap on the grating scale, and the beams are diffracted by the grating scale and interfere on the PD's. The period of the interference signal variation is just half of the scale grating period. The device was designed and fabricated with a grating scale of 3.2-[[micro]meter] period, and the sensing principle was experimentally confirmed. Key words: Integrated optics, thin-film waveguide, integrated optic sensor, grating coupler, displacement sensor, optical interferometer.

A packaging technique for an optical 90 degree-hybrid balanced receiver employs a silica-based planar lightwave circuit as optical couplers and two polarization beam splitters. The receiver contains two GRIN rod lenses that allow perfect optical interconnections. Fabrication by microsolder bump bonding remove parasitic elements in interconnections. A module gives an excellent performance with a broad-band frequency response of 14 GHz. It can achieve 10 Gb s binary phase shift keying homodyne detection.

An integrated structure of InAlAs InGaAs heterojunction bipolar transistor (HBT) and optical waveguide is applicable for optical control in monolithic microwave integrated circuit (MMIC) oscillators. The fabrication of a waveguide on the semiconductor surface enables delivery of light to the HBT. The fabricated waveguide-HBT structure exhibits cutoff and maximum frequencies of oscillation of 32 and 48 giga Hz, respectively. The MMIC oscillators exhibit optical tuning and injection locking at 13.9 giga Hz.

A theoretical and experimental investigation of a diffusion-cooled CO2 laser with a coaxial waveguide reveals that two annular plane mirrors enclose the two ends of the wave guide of the resonator, which extracts the laser beam through one of the apertures in these mirrors. Efficient beam extraction through this aperture is possible by the tilt of the mirror. The investigation reveals coaxial waveguide lasers and their ability to supply beams of high power and quality.

The study of ridge-waveguide multiple-quantum-well (MQW) was carried out by employing an efficient, newly developed, accurate technique. The method is based on the mode-matching transfer matrix method and the discrete spectral index technique. The derived technique adopts a semianalytical approach to the construction of three-dimensional ridge-waveguide semiconductor lasers. This technique is superior to earlier methods in terms of versatility, simplicity and adherence to accuracy.

Integrated optics techniques (i.e., guiding light through a thin film) have been used to study the effects of extended cure and moisture exposure on polyimide films as manifested in changes in the TE (in-plane) and TM (out-of-plane) refractive indices and in their difference (birefringence). Mechanical testing of these films has been done using the load-deflection technique. Du Pont polyimide Pyralin 2555 and 2556 (benzophenone tetracarboxylic dianhydride-oxydianiline/metaphenylene diamine), cured repeatedly at 400 [degrees] and 375 [degrees] C respectively, show an increase in refractive index as a function of cure (possibly due to densification), as well as an increase in birefringence (due to increased residual stress). Upon exposure to moisture, the TM and TE refractive indices both increase (absorption of the polar water molecule), but the TE index does not increase as much. Mechanical testing has shown that the residual stress in the polyimide film increases with extended cure and decreases with moisture exposure due to moisture-induced swelling of the film. A model is proposed which relates the optical results to the mechanical measurements. Based on our data, a preliminary stress-optic coefficient is reported.

We present an inexpensive, reusable method of introducing optical fibers into ultrahigh vacuum systems. A Teflon ferrule with a center-drilled hole slightly larger than the fiber diameter replaces the metal ferrules of a standard Swagelok connector. The Swagelok connector when tightened compresses the Teflon to form a vacuum seal for pressures of [less than or equal to]2 x [10.sup.-10] Torr.

A white-light reconstruction setup for shearograms using optical-fiber waveguides is presented. The setup is compact, is not susceptible to dust and scratches, and enables the two-dimensional fringe pattern on shearograms to be viewed directly under uniform and enhanced illumination with minimal image distortion.

Despite all the recent advances in laser technology, one dream device remains elusive: No one has yet figured out how to make a tabletop instrument that can pump out a […]